The present disclosure relates to a calibration system, a calibration method, and an image forming apparatus for correcting gradation characteristics.
In image forming apparatuses such as printers and multifunction peripherals (MFPs), calibration is performed for correction of input/output characteristics, that is, so-called gamma correction in order to compensate for changes due to aging and the like. A known calibration method involves measuring current output colors using a scanner mounted in an MFP or a density sensor in an image forming apparatus and correcting input/output characteristics such that the color values of the output colors will be desired color values.
However, an expensive, dedicated colorimeter such as a spectrocolorimeter is needed in order to match color values of output colors from an image forming apparatus with color values of output colors from a different type of image forming apparatus. It is however challenging for ordinary users to prepare and make full use of such a dedicated colorimeter.
In order to solve such a problem, calibration systems are offered that allow simple and low-cost calibration by using an imaging device such as a digital camera or a camera phone as a device alternative to the dedicated colorimeter.
In one example of the calibration systems, first, an imaging device captures an image of a reference chart containing patches of a plurality of colors together with an image of a test chart that corresponds to the reference chart and that is printed by an image forming apparatus. Next, gradation characteristics of the image forming apparatus are corrected based on RGB values of the respective patches in the reference chart and the test chart in a picture generated through the image capture by the imaging device.
In another example of a calibration system, first, an imaging device separately captures an image of a reference chart containing patches of a plurality of colors and an image of a test chart that corresponds to the reference chart and that is printed by an image forming apparatus. Next, first correction values are calculated based on color values of the patches in the reference chart in the first image captured by the imaging device and on color values of the patches in the test chart in the second image captured by the imaging device. Furthermore, second correction values are calculated based on the color values of the patches in the reference chart in the first image and on reference color values prestored in the image forming apparatus. Next, gradation characteristics of the image forming apparatus are corrected based on the first correction values and the second correction values.